The outpost was among many forming a protective ring around Kunduz city, which was briefly captured by the Taliban a year ago - the first time the armed group seized a provincial capital since losing power in 2001 after the US-led invasion.

In recent months, the Taliban have stepped up attacks across the country against Afghan security forces.

Insider attacks have plagued both Afghan and international troops in the country, depleting morale and causing mistrust within security ranks.

Authorities estimate about 5,000 Afghan police and troops were killed in 2015 - with an additional 15,000 wounded.

NATO, which helps to train and advise Afghan forces, warns the grim numbers are expected to increase this year.